1. Field of the Invention
The present invention relates to semiconductor manufacturing technology generally, and more particularly, to containing thermal interface material in heat spreader technology for heat dissipation in a semiconductor package.
2. Description of the Related Art
Semiconductor technology may be characterized as a quest to place more transistors on less space to achieve greater speed and performance. As integrated circuits and other semiconductor devices become faster, operating frequencies (i.e. clock speed in a microprocessor) also increase. At the same time, engineers and developers also strive to construct semiconductor devices that are more compact, therefore the distances between the conductive lines within the semiconductor device are being decreased accordingly.
As the density of conductive lines in and the clock speed of circuits increase, the amount of heat generated by the device also increases. Unfortunately, device reliability and performance decrease as the amount of heat increases, whether the heat is generated by the device or from other sources. In addition, semiconductor devices are prone to overheating, which is a point of heat tolerance past which, the device will fail and be unable to operate. Therefore, it is critical to have an efficient heat-removal system associated with integrated circuits. One conventional method to remove heat from a chip package is by using a heat spreader, which may also be used in combination with a second level solution.
FIG. 1 illustrates a conventional chip package 10. Chip package 10 includes a chip die 12 supported by a substrate 14. Substrate 14 is also able to support other various circuit components, such as capacitors 16. Chip package 10 also includes a heat spreader 18, which is coupled to chip die 12 through a thermal conductor known as a thermal interface material (TIM) layer 20. Heat spreader 18 is also attached to substrate 14 using a sealant 22. A second level solution, such as a heat sink (not illustrated) may also be coupled to heat spreader 18 to absorb heat generated from the circuitry in chip package 10.
Heat spreaders are becoming more and more important in semiconductor technology, particularly because semiconductor devices, including chip package 10, continue to become more compact. As devices continue to decrease in size, the performance of heat spreaders must continue to improve. Therefore, it is important to evenly distribute heat generated by chip package 10, which is the function of heat spreader 18, which typically comprises a ceramic material or a metal, such as aluminum or copper. Heat spreader 18 is coupled to chip die 12 and capacitors 16 through TIM layer 20.
Examples of TIM include polymer gel, grease or polymer/solder hybrid containing metal particles to improve heat conduction. Using a or solder in TIM layer 20 results in improved thermal conductivity, which is important for future microprocessors, which will generate even more heat. However, a disadvantage of using solder or a stiffer polymer in the TIM occurs in the process of forming the TIM itself. Unlike normal polymeric TIM, which is formed by curing and gelling, a solder or polymer/solder preform must be heated to form a liquid so that it may be evenly distributed on the bottom surface of heat spreader 18. However, during the time that the preform is in liquid form, it is difficult to control the flow of the thermal interface material.
FIG. 2 is a x-ray diagram illustrating a solder TIM layer 20 being formed in chip package 10. As described above, the preform solder is heated to form a liquid. After being heated, the liquid preform reflows to wet chip die 12 and cools to form TIM layer 20. Unfortunately, because the solder TIM assumes liquid form during the process and because the reflow is difficult to control, the liquid solder is likely to flow onto and build up on substrate 14 (illustrated in FIG. 1).
Often the reflow of liquid solder will enter areas reserved for other sensitive circuit components in chip package 10, such as capacitors 16. When the liquid TIM comes into contact with circuit components supported by substrate 14, the capacitors 16 will likely short circuit, leading to failure of chip package 10. In addition, the build up of excess TIM on substrate 14 may cause stress concentrations. The excess TIM may expand and contract, initiating cracks in substrate 14 on either the die to solder interface or the heat spreader to solder interface, resulting in a reduction in thermal performance.
In view of the foregoing, what is needed is a method and apparatus providing for the rapid dissipation of heat through a thermal interface material to a heat spreader. It is also desirable to provide for beading TIM evenly on a substrate surface and to prevent excess TIM from flowing into contact with sensitive parts of a chip package.